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Title: The Heart, Introduction and Evolution 1- We just looked at the composition and function of blood. However, for blood to reach each of the body cells and exchange material with them it must be constantly pumped by the heart through the body’s many miles of blood vessels 2- Interesting facts: a- Your heart beats about 100,000 times each day or about 35 million beats per year b- Live to be 85 (slightly more than average) and this equals about 2.98 billion beats c- Bill Gates could give you $40 each time your heart beats, for your whole life, and still have a few billion left over d- You have about 60 – 80 thousand miles (100,000 – 120,000 Km) of blood vessels e- Your heart pumps about 30X your own weight each minute (even while sleeping) f- The heart pumps 3,600 gallons of blood a day or 2.6 million gallons a year Animal Short Tailed Shrew Hummingbird Chicken Cat Human African Elephant Blue Whale Galapagos Tortoise Beats per Minute 1400 1360 275 150 60 30 18 6 Weight 3.6 grams 4.5 grams Life Expectancy 2 years 3 years 4-5 Tons 100 Tons 78 years 85 years 125 years * 180 years g- The heart of a blue whale weighs 1000 lbs, its aorta is 4.5 feet in diameter and its total blood weight is 1400 lbs * In 2003 a male Bowhead whale washed up in San Diego with a harpoon imbedded in its side manufactured between 1780-1790. It’s not believed that these types of harpoons were used after 1800. That would make the whale over 200 years old! He was born when Thomas Jefferson was president and died when Bill Clinton was president. 3- Evolution of the Heart – The heart is a marvel of evolution that ranges in function from the very simple heart of invertebrates such as worms, to the more complex structure of the squid to extremely complex animal hearts. a- Invertebrates 1- Worms – The heart of the worm is no more than a muscular tube that moves a blood-like material called hemocoele through the body via peristaltic action 2- Sea squirts pump blood in one direction for several minutes and then change its direction for several minutes 3- Mollusks have a 5 chambered heart (4 atria and 1 ventricle) 4- Annelids have 7 or more chambers 5- Squids have three separate hearts – 2 gill hearts that force blood under pressure to the gills and one heart that forces oxygen rich blood to the rest of the body 6- This diversity in structure is often explained by these organisms relative small size, low metabolic activity and that the role of the circulatory system is often less about respiratory exchange and more about nutrient exchange which can be designed with more flexibility 4- In vertebrates the primary role of the circulatory system is transporting oxygen to the cells. Therefore, a certain generalization of structure is necessary. Complexity increase from fish to amphibians to reptiles and mammals a- Vertebrates 1- Fish – a- The fish heart is the simplest of vertebrate hearts. b- It consists of two chambers, a thin walled atrium and a thicker muscular ventricle. In fish blood is moved from the atrium to the ventricles to the conus (tissue that does not pump but can be stretched and squeezed) c- From the conus the blood goes to the gills for oxygenation and then to the body and then back to the atrium d- Fish have a single circuit circulation 2- Amphibians – a- The amphibian heart is a more complex double loop circulation. Amphibians have three chambers: 2 atria and a common ventricle b- Amphibians have definitive aorta and pulmonary arteries projecting from the conus c- Both oxygen rich and poor blood are generally kept separate by well-timed contractions of the right and left atrium. However, there is sufficient mixing of the blood to produce “coldbloodedness” and a relatively slow metabolic rate 3- Reptiles a- Like amphibians, reptiles also have a three chambered, two loop circulation b- Reptiles have 2 atria and 1 partially divided ventricle – some people make the defensible argument that reptiles actually have a 4 chambered heart but that the ventricular wall separation is incomplete (ventricular septum (wall) defects as well as atrioventricular septum defects are common in people) Both arguments are reasonable c- As in amphibians there is mixing of the oxygen rich and oxygen poor blood. However, this mixing is minimized by timing of contractions and the partial wall. d- Crocodiles are the lone exception among reptiles (as well as all animals). The crocodile has a four chambered heart with full ventricular separation (like birds and mammals). However the right ventricle can pumps blood through two different vessels: the pulmonary artery and the right systemic artery i. By opening or closing a flap of tissue called the “Foramen of Panizza” a crocodile can effectively switch between normal and low oxygen conditions. He does this by shutting off oxygen to the pulmonary circulation. ii. When underwater oxygenated blood is shunted away from the lungs and mixes with oxygen rich blood exiting the right aorta to other vital organs in the body iii. Franklin and Axelsson two of the leading experts on crocodile anatomy say that it is the most advanced heart of any animal alive today 4- Birds and Mammals (including humans) a- Birds and mammals are endothermic (warm blooded) with a high metabolic rate and an efficient two-looped closed circulation (pulmonary and systemic). Both birds and mammals have 4 separate chambers: 2 atrium and 2 ventricles. There is no mixing of oxygenated and deoxygenated blood in the normal heart (No AVM malformations or interatrial, or interventricuar malformations) b- In birds and mammals: 1- Deoxygenated blood enters the right atrium through the common vena cava (formed from the union of the superior and inferior vena cava) 2- The deoxygenated blood then passes through the tricuspid valve into the right ventricle 3- Deoxygenated blood is then pumped out of the right ventricle through the pulmonary valve into a large artery called the pulmonary trunk, which then branches into the right and left pulmonary arteries to the lungs for oxygenation 4- The left atrium receives the newly oxygenated blood returning from the lungs through the four pulmonary veins 5- The oxygenated blood then passes through the biscuspid (mitral) valve into the left ventricle 6- The left ventricle (the thickest part of the heart) contracts and pushes blood through the aortic valve into the ascending aorta (some of the blood flows from the ascending aorta to the coronary arteries to nourish the heart) the blood then passes into the aortic arch, where it branches into the brachiocephalic trunk, the left common carotid artery, the left subclavian artery and the descending aorta.